This invention relates to heat exchangers and more particularly to a device for guiding fluid flow around a tube bundle in a heat exchanger.
The invention makes possible the improvement in the heat transfer at a low pressure drop and the simple threading of the individual tubes in mounting the tube bundle apparatus.
Without any guiding device, media flow on the exterior of a tube bundle within a casing is parallel to the tubes. Also, without any flow guiding device, the velocity distribution is non-uniform over the outer surface of the tubes so that, in relationship to the pressure loss, low heat transfer figures are produced.
As is known, the heat transfer increases less than proportionally to the velocity, whilst the pressure loss increases considerably more than proportionally, practically quadratically.
Furthermore it is known that the heat transfer when the tubes are subject to cross flow is considerably increased with respect to the heat transfer which can be achieved with longitudinal flow.
Guide means for providing a better distribution of the flow velocity and, above all, for providing partial cross flow, are known in the form of so-called fittings or baffles.
However, the guide means known up till now have considerable deficiencies. They provide a low heat transfer and yield but a disproportionately high pressure loss.
In addition, there exist with the known guide means, zones of low flow velocity in which the danger of deposit formations is increased.
Among other things, segmented circular baffles are known which are mounted in the external space transverse to the axes and at uniform distances from one another and with the edges of the segments against one another.
These guide means force the medium to flow to and fro in the external space thus, in part transversely with respect to the tubes, whereby the medium flows around the edges of the segments at more or less 180.degree.. This enforced change in direction of 180.degree. produces very non-uniform velocity distributions and partial longitudinal flows in the external space so that an improvement in the heat transfer corresponding to the pressure loss cannot be achieved.
Moreover, so-called disc fittings are known in the heat exchanger art. Normally, these discs have a circular opening in the center so that the flow can pass through and toward a baffle plate of larger diameter than the central opening in the preceding disc.
With the disc guiding means, the medium flowing in the external space is only partially guided transversely with respect to the fitted tubes and the changes in direction of 180.degree. worsen the ratio of the heat transfer to the pressure loss in the same manner as with the segmented means.